Temperature measurement system for furnaces

ABSTRACT

A method for measuring furnace temperatures. The method includes obtaining radiance measurements from a plurality of regions of interest (ROIs) using a plurality of thermal imaging cameras, and measuring a surface temperature using a radiance measurement obtained from an ROI selected from the plurality of ROIs. Measuring the surface temperature includes determining an effective background radiance affecting the selected ROI using radiance measurements obtained from ROIs different from the selected ROI, obtaining a compensated radiance by removing the effective background radiance from the radiance measurement obtained from the selected ROI, and converting the compensated radiance to the measured surface temperature.

BACKGROUND

Availability of local temperature measurements from within a furnace,e.g., a reformer furnace, may be critical for the operation of thefurnace. Such temperature measurements may be obtained using radiationthermometry. However, the accuracy of radiation thermometry measurementsmay be adversely affected by the conditions within the furnace.

SUMMARY

In general, in one aspect, the invention relates to a method formeasuring furnace temperatures. The method includes obtaining radiancemeasurements from a plurality of regions of interest (ROIs) using aplurality of thermal imaging cameras, and measuring a surfacetemperature using a radiance measurement obtained from an ROI selectedfrom the plurality of ROIs. Measuring the surface temperature includesdetermining an effective background radiance affecting the selected ROIusing radiance measurements obtained from ROIs different from theselected ROI, obtaining a compensated radiance by removing the effectivebackground radiance from the radiance measurement obtained from theselected ROI, and converting the compensated radiance to the measuredsurface temperature.

In general, in one aspect, the invention relates to a non-transitorycomputer readable medium storing instructions for measuring furnacetemperatures. The instructions include functionality for obtainingradiance measurements from a plurality of regions of interest (ROIs)using a plurality of thermal imaging cameras and measuring a surfacetemperature using a radiance measurement obtained from an ROI selectedfrom the plurality of ROIs. Measuring the surface temperature includesdetermining an effective background radiance affecting the selected ROIusing radiance measurements obtained from ROIs different from theselected ROI, obtaining a compensated radiance by removing the effectivebackground radiance from the radiance measurement obtained from theselected ROI, and converting the compensated radiance to the measuredsurface temperature.

In general, in one aspect, the invention relates to a system formeasuring furnace temperatures. The system includes a plurality ofthermal imaging cameras and a processing unit. The processing unit isconfigured to obtain radiance measurements from a plurality of regionsof interest (ROIs) using the plurality of thermal imaging cameras, andmeasure a surface temperature using a radiance measurement obtained froman ROI selected from the plurality of ROIs. Measuring the surfacetemperature includes determining an effective background radianceaffecting the selected ROI using radiance measurements obtained fromROIs different from the selected ROI, obtaining a compensated radianceby removing the effective background radiance from the radiancemeasurement obtained from the selected ROI, and converting thecompensated radiance to the measured surface temperature.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1C show temperature measurement systems for measuringtemperatures inside a furnace, in accordance with one or moreembodiments of the invention.

FIGS. 2-4 show a flowchart in accordance with one or more embodiments ofthe invention.

FIG. 5 shows a computer system in accordance with one or moreembodiments of the invention.

DETAILED DESCRIPTION

Specific embodiments of the invention will now be described in detailwith reference to the accompanying figures. Like elements in the variousfigures are denoted by like reference numerals for consistency.

In the following detailed description of embodiments of the invention,numerous specific details are set forth in order to provide a morethorough understanding of the invention. However, it will be apparent toone of ordinary skill in the art that the invention may be practicedwithout these specific details. In other instances, well-known featureshave not been described in detail to avoid unnecessarily complicatingthe description.

Throughout the application, ordinal numbers (e.g., first, second, third,etc.) may be used as an adjective for an element (i.e., any noun in theapplication). The use of ordinal numbers is not to imply or create anyparticular ordering of the elements nor to limit any element to beingonly a single element unless expressly disclosed, such as by the use ofthe terms “before”, “after”, “single”, and other such terminology.Rather, the use of ordinal numbers is to distinguish between theelements. By way of an example, a first element is distinct from asecond element, and the first element may encompass more than oneelement and succeed (or precede) the second element in an ordering ofelements.

In the following description of FIGS. 1A-5, any component described withregard to a figure, in various embodiments of the invention, may beequivalent to one or more like-named components described with regard toany other figure. For brevity, descriptions of these components will notbe repeated with regard to each figure. Thus, each and every embodimentof the components of each figure is incorporated by reference andassumed to be optionally present within every other figure having one ormore like-named components. Additionally, in accordance with variousembodiments of the invention, any description of the components of afigure is to be interpreted as an optional embodiment which may beimplemented in addition to, in conjunction with, or in place of theembodiments described with regard to a corresponding like-namedcomponent in any other figure.

In general, embodiments of the invention relate to a system and methodsfor measuring temperatures from image data, using radiation thermometry.More specifically, accurate temperature measurements of a region ofinterest (ROI) may be obtained by correcting thermal radiance data,obtained from one or more thermal imaging cameras, for various factorsthat would otherwise negatively affect the accuracy of the temperaturemeasurement. These factors include, but are not limited to, backgroundradiation, e.g., radiation originating from other heat sources, that isreflected by the ROI, atmospheric attenuation, flame enhancementeffects, the geometric configuration of the environment in whichmeasurements are obtained, and the emissivity of the ROI being measured.The methods used to correct for these factors are described in detailbelow.

In one or more embodiments of the invention, the corrections may beperformed in real-time or in near real-time, thus resulting in accuratetemperature measurements even in dynamically changing environments.

The corrections may be performed for multiple ROIs within the thermalimaging camera's field of view, or for multiple ROIs within multiplecameras' fields of view, in accordance with one or more embodiments ofthe invention. Although the corrections for different ROIs may beperformed separately for each ROI, interdependencies between ROIs,further described below, may be considered.

FIGS. 1A-1C show temperature measurement systems (100) in accordancewith one or more embodiments of the invention. FIG. 1A shows a top viewof an exemplary furnace (102) and thermal imaging cameras (150). FIG. 1Bshows a side view into the furnace (102). The view shown in FIG. 1B isan example of a view that a thermal imaging camera (150) may have intothe furnace (102), through a sight door (110). A thermal imaging camera,positioned to capture images from the interior of the furnace, mayobtain such a view. FIG. 1C shows a top view detail of the exemplaryfurnace of FIG. 1A. The furnace may be, for example, a reformer furnaceof a steam reformer that may be used to produce hydrogen and/or otherindustrial gases and fuels. The interior of the furnace (102) may beenclosed by a set of furnace walls (104). A set of reformer tubes (108)may traverse the interior of the furnace. In FIGS. 1A and 1B, thereformer tubes (108) vertically traverse the furnace from the floor(112) to the ceiling (not shown) of the furnace (102). Alternatively oradditionally, reformer tubes (108) may traverse the furnace in any otherorientation, e.g., horizontally. A catalytic reaction may take placewithin the reformer tubes (108). This catalytic reaction may be, forexample, a reaction of a combination of steam and hydrocarbons intohydrogen and carbon monoxide and further to more hydrogen and carbondioxide. The reaction, to take place, may rely on an external source ofheat. In one embodiment of the invention, the external source of heat isprovided by heating the reformer tubes (108) by combustion of oil orgas, e.g. natural gas, inside the furnace (102). The furnace may betop-fired, wall-fired and/or bottom-fired by burners (106).

The reformer tubes (108) may be metal tubes. These metal tubes may beexposed to high temperatures and/or high pressures. Depending on thetype of reforming being performed, temperatures may be in the range of1,000° C. and pressures may reach 100 bar. Under these conditions, thereformer tubes (108) may age. Aging may be accelerated if hot spotsexist in the reformer tube walls. To prolong the life of the reformertubes and to avoid the risk of potentially catastrophic failures, onemay therefore want to regulate the furnace to avoid hot spots, forexample, by making local adjustments of the fuel flow to the burners. Itmay therefore be necessary to measure temperatures inside the furnace(102). To detect hot spots in the reformer tube walls, it may bedesirable to obtain surface temperatures of the reformer tubes. In oneembodiment of the invention, regions of interest (ROIs) (114) from wheretemperature measurements are to be obtained therefore include multiple(many) regions on the surface of the reformer tubes. Further,temperature measurements may also be obtained from the furnace walls(104), the furnace floor (112), the furnace ceiling (not shown), etc.ROIs (114) may be located virtually on any target object in and/or onthe furnace (102). Those skilled in the art will recognize that while inFIGS. 1A-1C the temperature measurement system (100) is shown as beingused for measuring temperatures in a reformer furnace, the systems andthe methods may be used in any other type of furnace, but also innon-furnace environments, without departing from the invention.

Continuing with the discussion of FIG. 1, the temperature measurementsystem (100) being used to measure surface temperatures in the furnace(102) includes thermal imaging cameras (150). The thermal imagingcameras may be positioned and oriented such that one or more regions ofinterest (ROIs) (114) are within the field of view of the thermalimaging cameras. Multiple cameras may be used to reach all desired ROIs(114) in the furnace (102). The thermal imaging camera(s) (150) may belocated outside the furnace (102) and may get a view of the inside ofthe furnace through a port in one of the furnace walls (104). Theexemplary furnace shown in FIG. 1A, is equipped with sight doors (110).A camera (150), installed outside of the furnace, may get a view of theinside of the furnace through one of the sight doors (110). Depending onthe location of the ROIs (114), multiple sight doors (110) may beequipped with cameras (150). A sight door, in accordance with anembodiment of the invention may be equipped with a bore scope lens thatmay be cooled. Further, additional measures may be taken to mechanicallyand thermally protect the thermal imaging cameras (150). For example, acontrol system may automatically retract a thermal imaging camera and/orlens if the cooling of the camera is compromised.

The thermal imaging camera may be any kind of radiation thermometer thatmeasures radiant power in a certain spectral range. The thermal imagingcamera may be, for example, a CCD camera, where each pixel provides aradiation measurement, or it may be a pyrometer providing a singleradiation measurement only. The incident thermal radiation may bereceived from regions in the field of view of the camera system,including the ROIs (108). An ROI may be represented by one or morepixels of the thermal imaging camera (150). An ROI within the field ofview may be defined during the setup of the system. During the setup, anoperator may select a set of pixels that correspond to a particularregion in the furnace, e.g. the surface of a reformer tube and mayassign them to an ROI. For example, an image, displaying the measuredthermal radiance values, may be shown to the operator, and the operatormay mark ROIs, e.g., by placing rectangles, circles, etc., in thedisplayed image. Pixels that fall into a marked region may then beconsidered to form an ROI. Thus, measurements of incident radiation,obtained from these individual pixels, are processed as measurementsbelonging to the ROI, as described in FIG. 3, and may be used asmeasurements of the thermal radiance of the ROI. A separate thermalradiance value may be obtained for each pixel of the thermal imagingcamera. The incident radiation, captured by the thermal imaging camera,may be thermal radiation limited to a range of wavelengths, e.g., toinfrared thermal radiation at a wavelength of 3.9 μm and/or 850 nm.Those skilled in the art will appreciate that any wavelength may beselected, based on criteria of the application. In particular, awavelength may be selected to accommodate known atmospheric conditionsin the furnace. For example, the wavelength may be selected to avoidwavelengths where water vapor absorption effects are known to exist, ifthe furnace atmosphere contains significant amounts of water vapor.Similarly, a wavelength may be picked to reduce flame enhancementeffects if measurements are performed through an area of the furnacewhere burners are installed.

Analog or digital signals that correspond to the amount of capturedincident radiation may be obtained for each pixel of the thermal imagingsystem. The analog or digital signals may be forwarded to a processingunit (160), where the temperature measurement, in accordance with anembodiment of the invention, is performed.

In one or more embodiments of the invention, the thermal imaging camera(150) and the processing unit (160) are calibrated to accurately measurethe temperature, using the following simplifying assumptions: (i) thethermal imaging camera may respond to a single wavelength only.Accordingly, a monochromatic approximation that states that the signal,obtained by the thermal imaging camera in response to the incidentradiation, is proportional to the spectral radiance of the targetedregion of interest (ROI), may be used; and (ii) the measured ROI isassumed to be a blackbody. Using these assumptions, a measuredtemperature, T_(m), may be calculated from the measured thermal imagingcamera signal, S_(m), using the following function:

$\begin{matrix}{{T_{m} \approx \frac{- c_{2}}{\lambda\mspace{14mu}\ln\mspace{14mu} s_{m}}},} & (1)\end{matrix}$where c₂=0.014388 mK, is the second radiation constant, used in Planck'slaw. Accordingly, the unit of temperature resulting from application ofEquation (1) is Kelvin. Equation (1) is a result of using Wien'sapproximation to Planck's law.

Further, the function

$\begin{matrix}{S_{m} \approx \frac{- c_{2}}{e^{\lambda\; T_{m}}}} & (2)\end{matrix}$may be used to calculate the measured signal of the thermal imagingcamera from the measured temperature.

In Equations (1) and (2), the measured temperature, T_(m), may onlymatch the actual temperature of a target body, if the target body is ablackbody. For any non-blackbody, the measured temperature, T_(m), maydeviate from the actual temperature of the measured target body. Themeasured temperature, T_(m), in accordance with an embodiment of theinvention, therefore is a radiance temperature. The radiance temperaturemay be understood as the temperature of a blackbody with the samespectral radiance as the actual measured body. Accordingly, the radiancetemperature, T_(m), may frequently deviate from the actual temperatureof the target body because typical target bodies are not blackbodies.

Continuing with the discussion of FIGS. 1A-1C, the processing unit(160), in accordance with an embodiment of the invention, is a computingdevice configured to execute at least one of the steps of the methodsdescribed in FIGS. 2-4. The processing unit may, for example, correctthe signals, received by a thermal imaging camera from an ROI, forbackground radiation, atmospheric absorption, the geometricconfiguration of the environment in which measurements are obtained, andthe emissivity of the ROI being measured, as subsequently described.

The furnace detail shown in FIG. 1C illustrates how background radiationmay affect the measurement of a temperature in an ROI (114) on thesurface of a reformer tube (108). The thermal imaging camera (150)receives radiation from the ROI (solid arrow), directed from the ROI tothe thermal imaging camera. However, the reformer tube (108) is exposedto background radiation from other surfaces in the furnace, as indicatedby the dashed arrows. In FIG. 1C, the source of this backgroundradiation is the furnace wall (104). In general, any type of object,including, but not limited to, other reformer tubes, a floor, a ceilingand/or a flame may direct background radiation toward the reformer tube.In FIG. 1C, any surface in a semicircle in front of the ROI, i.e., inthe angular range −90°<Θ_(in)<90°, as indicated by the dotted line inFIG. 1C, may be considered as directing background radiation toward theROI. In the general case of 3D environments, any surface in a hemispherein front of the ROI may be considered as directing background radiationtoward the ROI.

Because the reformer tube may reflect background radiation, theradiation signal received by the thermal imaging camera from the ROI mayinclude the reflected background radiation. The radiation signalreceived by the thermal imaging camera therefore needs to be adjustedfor the reflected background radiation, in order to obtain an accuratemeasurement of the temperate in the ROI, in accordance with one or moreembodiments of the invention. A compensation may be performed byestimating the background radiation that the ROI is exposed to, and byremoving this estimated radiation component, as described in detailbelow, with reference to FIG. 4. These steps may be performed by theprocessing unit (160).

The processing unit (160) may interface with industrial monitoring andcontrol systems, for example, via the Open Process Control (OPC)interoperability standard for industrial automation. Output of theprocessing unit (160), obtained by execution of one or more of thesubsequently described methods may thus be used to monitor and controlthe furnace (102), and/or to enhance process performance in general. Theprocessing unit (160) may include functionality for generating alarms iftemperature windows, specified for monitored ROIs, are exceeded.Further, the processing unit may include functionality for archivingtemperature data obtained from the ROIs. The archived temperature datamay include thermal radiance values, recorded by a thermal imagingcamera, and/or temperature measurements, calculated using one or more ofthe methods described below. Further, the processing unit may include avisualization unit to present the thermal radiance values and/or themeasured temperatures to an operator, using, for example, a textual orgraphical representation such as a heat map.

In one embodiment of the invention, the processing unit (160) is acomputing system similar to the one described in FIG. 5.

Those skilled in the art will appreciate that although theabove-described temperature measurement system is introduced in thecontext of a reforming furnace, temperature measurement systems may beused in other scenarios without departing from the invention. Forexample, temperature measurement systems, in accordance with one or moreembodiments of the invention, may be used to monitor and/or controlboilers and other types of furnaces such as annealing furnaces,reheating furnaces, ovens, etc. Further, a temperature measurementsystem may be scaled as need or desired. For example, all regions ofinterest (ROIs) in a small furnace with a simple geometry may becaptured by a single thermal imaging camera. Accordingly, a basictemperature measurement system may have only a single thermal imagingcamera. In contrast, a large furnace with a complex geometry may requiremany cameras to capture all ROIs. Accordingly, a larger temperaturemeasurement system may rely on image data from a network of many thermalimaging cameras.

FIGS. 2-4 show flowcharts in accordance with one or more embodiments ofthe technology. FIG. 2 shows a method for configuring the temperaturemeasurement system for performing temperature measurements. FIGS. 3 and4 show methods for performing the temperature measurement, in accordancewith one or more embodiments of the invention.

While the various steps in the flowcharts are presented and describedsequentially, one of ordinary skill will appreciate that some or all ofthese steps may be executed in different orders, may be combined oromitted, and some or all of the steps may be executed in parallel. Inone embodiment of the technology, the steps shown in FIGS. 2-4 may beperformed in parallel with any other steps shown in FIGS. 2-4 withoutdeparting from the technology.

FIG. 2 shows a method for configuring the temperature measurement systemfor performing temperature measurements. The steps described in FIG. 2may be executed once during the setup of the temperature measurementsystem. Alternatively, one or more of the steps described in FIG. 2 maybe executed periodically, e.g., as the methods described in FIGS. 3 and4 are executed.

Turning to FIG. 2, in Step 200, the thermal imaging camera(s) is/arecalibrated. The calibration is performed by measuring a blackbody (e.g.,a blackbody cavity) at a known temperature point or at multiple knowntemperature points. The gain(s) of the thermal imaging camera(s) maythen be adjusted such that the radiance temperature(s) indicated by thecamera(s) match(es) the blackbody temperature(s). The calibration ofStep 200 may be performed inside the furnace after the cameras have beeninstalled, for example, if a reference body is installed in the furnace,or outside the furnace, prior to installation of the cameras.

In Step 202, potential atmospheric absorption and/or emission effects inthe furnace are determined. Atmospheric absorption may occur if theatmosphere between the region of interest (ROI) being measured and thecamera, at the wavelength used for performing the measurements, isabsorbent. The degree of absorption may depend on the concentration ofthe gases that cause the absorption and on the distance between the ROIand the camera. The absorption may be determined based on measurementsor based on known characteristics of the furnace atmosphere. Ameasurement-based determination of the absorption may be performed, forexample, by measuring the radiance of an ROI in the furnace fromdifferent distances. The difference in the obtained radiancetemperatures (lower radiance temperature for longer distance; higherradiance temperature for shorter distance) may be used to determine theatmospheric attenuation, assuming a particular relationship betweendistance and atmospheric absorption. This relationship may be assumed tobe linear. Alternatively, the attenuation may be modeled, if the furnaceatmosphere is understood. For example, it may be known that the furnaceatmosphere contains a certain level of water vapor which, at thewavelength used for the measurements, causes a certain attenuation ofthe radiation over a certain distance. An absorption coefficient may beused to quantify the attenuation effect, determined in Step 202.

Similarly, atmospheric emissions may affect the accuracy of themeasurement. Emission effects may occur, for example, if the atmospherebetween the ROI being measured and the camera includes a flame. A flamemay have a characteristic spectral emission spectrum. If this spectrumreaches overlaps with the wavelength used for performing themeasurements, the measurement of the ROI's temperature may beexaggerated due to the radiation emitted by the flames. Accordingly,measurements performed through flames may require compensation for theatmospheric emissions caused by the flames. The flame enhancement effectmay be measured or modeled, based on known characteristics of thefurnace atmosphere. A measurement-based determination of the enhancementmay be performed, for example, by measuring the same ROI in the furnacefrom different distances. The difference in the obtained radiancetemperatures (higher measured radiance temperature for longer distance;lower measured radiance temperature for shorter distance) may be used todetermine the atmospheric emissions, assuming a particular relationshipbetween distance and atmospheric emission. This relationship may, forexample, be assumed to be linear. Alternatively, the atmosphericemissions may be modeled based on known absorption characteristics, forexample, of the fuel being burned. The model-based determination may beperformed in real-time, as the methods described in FIGS. 3 and 4 areperformed. In one embodiment of the invention, if a flame front isbetween a camera and a region of interest (ROI) being measured by thecamera, the width of the traversed flame front may be considered, andthe fuel flow to the burners associated with the flame front may bemetered, such that, based on fuel flow and the type of fuel, theatmospheric conditions in the flame area and the correspondingatmospheric emissions can be modeled, thus enabling a dynamicallycorrectable compensation for the atmospheric emissions. An emissioncoefficient may be used to quantify the emission effect, determined inStep 202.

In Step 204, the emissivity, ε, of the surface in the ROI(s) isdetermined. Various methods may be used to assess the emissivity of anROI being measured. The emissivity may, for example, be obtained fromthe literature, based on the material and surface characteristics in theROI. Alternatively, the emissivity may be measured. Emissivitymeasurements may be performed once, e.g., when the temperaturemeasurement system is installed, or periodically during the operation ofthe temperature measurement system. In one embodiment of the invention,the emissivity is determined based on a thermal radiance measurementobtained from the ROI and a thermal radiance measurement obtained from areference body with a known emissivity, e.g., a blackbody that is knownto have the same temperature as the target surface, in the ROI. Based onthe discrepancy between the measured thermal radiance of the blackbodyand the measured thermal radiance of the ROI, a gain factor, correctingfor the difference in radiances received from the blackbody and thetarget surface, in the ROI, is determined. The inverse of the gainfactor may be used as the emissivity of the target body in the ROI.Alternatively or in addition, a temperature sensor, e.g., athermocouple, installed in the vicinity of the ROI may serve as atemperature reference for the purpose of determining an emissivity inthe ROI. If the emissivity is determined periodically, Step 204 may beperformed as part of the method described in FIG. 4.

FIG. 3 shows a method for measuring a temperature using thermal radiancemeasurements obtained from one or more thermal imaging cameras, inaccordance with an embodiment of the invention. The method of FIG. 3 maybe executed once to obtain one or more temperature measurements.Alternatively, the method may be executed repeatedly to obtainrepeatedly updated temperature measurements. In one embodiment of theinvention, the method may be used to continuously obtain temperaturemeasurements in real-time or near-real-time, i.e., immediately after theradiance measurements were performed.

In Step 300, thermal radiance measurements are obtained from regions ofinterest (ROIs) inside the furnace. One thermal radiance value may beprovided per pixel. Accordingly multiple thermal radiance measurementsmay be simultaneously received for a single ROI. Further, repeatedmeasurements may be performed over a time interval. In one embodiment ofthe invention, the measurements are averaged to obtain a single thermalradiance measurement per ROI. Averaging may be performed over multiplepixels of the ROI and/or over time. The spatial averaging may considerthe measurements obtained from all pixels of the ROI, or it may onlyconsider measurements from a subset of the pixels. If measurements areperformed in order to identify hotspots, no spatial averaging may beperformed. Temporal averaging may be performed over a time interval thatmay include multiple measurements. For example, thermal radiance valuesfrom multiple consecutively recorded camera frames may be averaged,e.g., over one second or multiple seconds, to reduce the effect ofshort-term temperature fluctuations.

The spatial and/or temporal averaging may be performed for thermalradiance measurements. If the measurements, provided by the thermalimaging camera(s) are radiance temperatures, the radiance temperaturesmay be converted to thermal radiance values using Equation (2), prior toperforming the averaging. Subsequently, Equation (1) may be used toconvert the thermal radiance value to a radiance temperature, ifdesired. Step 300 may be performed for multiple or all ROIs in thefurnace, resulting in a set of radiance temperature measurements and/orthermal radiance measurements.

In Step 302, measurements for the surface temperatures in the regions ofinterest (ROIs) are obtained from the thermal radiance measurements, inaccordance with one or more embodiments of the invention. The thermalradiance measurements, obtained in Step 300, are corrected forenvironment-specific effects, and temperature measurements for the ROIsare derived from the corrected thermal radiance measurements. Thecorrections performed in Step 302 may include, but are not limited to,corrections for the emissivities of the surfaces in the ROIs,corrections for atmospheric absorption and/or emission effects in thefurnace, and corrections reducing the effect of background radiationoriginating from other regions in the furnace, that is reflected by theROIs. The details of Step 302 are described in FIG. 4.

In Step 304, the temperature measurements, obtained for the ROIs, arereturned. These temperature measurements, after the correctionsperformed in Step 302, are assumed to accurately represent surfacetemperatures in the ROIs. The temperature measurements may be reportedto a user and may, for example, be displayed in a spreadsheet and/or ina graphical visualization, e.g., in a heat map. Further, the temperaturemeasurements may be archived, for example on a hard disk drive. Thetemperature measurements may further be used to control the operation ofthe furnace. In regions where excessive heat is detected, adjustmentsmay be made to reduce the fuel flow to the burner(s), and in regionswhere temperatures are determined to be too low, the fuel flow to theburner(s) may be increased.

FIG. 4 shows a method for measuring surface temperatures in the regionsof interest (ROIs), from the thermal radiance measurements obtained fromthese ROIs. The measurement, in accordance with one or more embodimentsof the invention, corrects for environment-specific effects that mayotherwise cause uncorrected radiance temperatures to deviate from theactual surface temperatures in the ROIs. In order to perform acorrection of a single thermal radiance measurement obtained from aparticular ROI, measurements from other ROIs within the furnace may berelied upon, as subsequently described.

In Step 400, an ROI, for which a surface temperature is to be measured,is selected. Many ROIs may be monitored in a furnace, in accordance withan embodiment of the invention. For example, the reformer furnaceoperator may want to know the surface temperatures of all reformertubes. Accordingly, at least one ROI may be located on each of thereformer tubes, and in addition on walls, the floor, the ceiling, flamefronts, etc. A selected ROI may thus be one of the ROIs located on oneof the reformer tubes.

In Step 402, the surrounding surfaces to be considered in thesubsequently performed measurement of the surface temperature areidentified. A surrounding surface may be a surface of another object inthe reformer furnace. In one embodiment of the invention, the radianceof surrounding surfaces affects the radiance temperature measurementobtained from the ROI. In general, only surfaces in a hemisphere infront of the ROI may need to be considered in Step 402, as previouslydiscussed with reference to FIG. 1C. Accordingly, the surroundingsurfaces, identified in Step 402, may be specific to the ROI selected inStep 400. For example, in a scenario in which an ROI, located on areformer tube, only faces a wall, a floor and a ceiling, only the wall,the floor and the ceiling may be considered surrounding surfaces. Allother surfaces in the furnace, whether ROIs are placed on them or not,may be ignored. In contrast, in another scenario in which an ROI,located on a reformer tube, in addition faces a segment of a secondwall, an adjacent reformer tube and a dirty flame (e.g., a flame thatproduces a considerable amount of soot), all of these surfaces may beconsidered surrounding surfaces.

In Step 404, a mean radiance is determined for each of the surroundingsurfaces to be considered. The mean radiance of a surrounding surfacemay be determined based on a radiance measurement obtained from an ROIlocated on the surrounding surface. If multiple ROIs are placed on asingle surface, a mean radiance may be obtained by calculating the meanof the radiances, obtained from the ROIs. Different ROIs may be weighteddifferently and/or one or more of the ROIs may be entirely ignored whenobtaining the mean radiance.

In Step 406, a geometric view factor is determined for each of thesurrounding surfaces to be considered. Generally, a geometric viewfactor for a particular surrounding surface may be understood as aweight to be applied to the corresponding mean radiance obtained in Step404. Using the geometric view factors obtained in Step 406 and the meanradiances obtained in Step 404, a weighted radiance average may becalculated, as described in Step 408. A geometric view factor may bedetermined using the following surface integral over the ith surroundingsurface, A_(i):

$\begin{matrix}{{{\mathcal{g}}_{i} = {\frac{1}{\pi}{\int{\int_{A_{i}}{\cos\mspace{14mu}\Theta_{in}d\;\omega_{in}}}}}},} & (3)\end{matrix}$where g_(i) is the geometric view factor of the ith surrounding surface.A small element of an area, dA, on the surface, A_(i), is located at theangle Θ_(in). Θ_(in), as previously described with reference to FIG. 1C,is the angle between the considered surface element and the normal tothe target surface at the measurement location. dA subtends the smallangle dω_(in), at the measurement location. The geometric view factorsof all considered surrounding surfaces sum to 1.

Equation (3) assumes an isotropically diffuse surface, in the ROI, i.e.,a surface that equally reflects radiation in all directions. If thisassumption is not justifiable, angular dependencies may be considered.These angular dependencies may be described using a bi-directionalreflectance distribution function (BRDF), where the reflectance is afunction of the polar and azimuthal angle describing the incidentradiation and a polar and azimuthal angle specifying the direction ofthe reflected radiation. For surfaces that are not completelyisotropically diffuse, the BDRF may thus be included in the equation forthe geometric view factor.

In Step 408, the effective background radiance is determined. Theeffective background radiance, in accordance with an embodiment of theinvention, is a weighted sum of the mean radiances of the surroundingsurfaces to be considered, determined in Step 404. The weighting isperformed using the geometric view factors obtained in Step 406.Accordingly:S _(b)=Σ_(i=1) ^(N) g _(i) Ss _(i)  (4),where S_(b) is the effective background radiance signal, N is the numberof considered surrounding surfaces, and Ss_(i) is the mean radiancesignal of the ith surrounding surface.

In Step 410, the effective background radiance signal is removed fromthe radiance measured in the ROI, using

$\begin{matrix}{{S_{s} = \frac{s_{m} - {\left( {1 - ɛ} \right)s_{b}}}{ɛ}},} & (5)\end{matrix}$where S_(s) is the radiance signal received from the ROI on the surfaceof the selected reformer tube, after subtraction of the reflectedbackground radiance, and where εis the emissivity of the surface in theROI. Accordingly, S_(s) is the radiance emitted by the reformer tube dueto the reformer tube's temperature, in the ROI, in accordance with oneor more embodiments of the invention.

In Step 412, a correction for atmospheric absorption and/or emissioneffects is performed. The correction may be performed by dividing thecompensated radiance signal by the absorption and/or emissioncoefficient, obtained in Step 202. Step 412 may be performed to addressatmospheric effects that would otherwise result in erroneous temperaturemeasurements. More specifically, the correction for atmosphericabsorption addresses effects that would result in depressed temperaturemeasurements, whereas the correction for atmospheric enhancementaddresses effects that would result in inflated temperaturemeasurements. As previously described in Step 202, the correction mayconsider the composition of the atmosphere, the distance between the ROIand the camera, and may dynamically update based on predictedatmospheric changes, e.g., based on the type of burner fuel, the lengthof the flame front traversed in a measurement, the fuel flow to theburner, etc.

In Step 414, the compensated radiance signal is converted to a surfacetemperature. Equation (1) may be used for the conversion. Steps 410-414may be performed on the averaged radiance signal obtained from theentire selected ROI. Alternatively or additionally, Steps 410-414 may beperformed on a radiance signal obtained from a single pixel orseparately from multiple pixels within the selected ROI. Performingthese steps on single pixel measurements may allow the determination ofa surface temperature with a high spatial resolution, for example, inorder to detect local hotspots on the surface of the reformer tubes.

In Step 416, a determination is made about whether additional ROIs areremaining for which a surface temperature measurement is to be obtained.Such ROIs may be located, for example, on other reformer tubes. If adetermination is made that additional ROIs are remaining the method mayreturn to Step 400. If no more ROIs are remaining, the method mayterminate.

While the various steps in the flowchart are presented and describedsequentially, one of ordinary skill will appreciate that some or all ofthese steps may be executed in different orders, may be combined oromitted, and some or all of the steps may be executed in parallel. Inone embodiment of the invention, the steps shown in FIG. 2 may beperformed in parallel with any other steps shown in FIG. 2 withoutdeparting from the invention.

Embodiments of the invention may enable accurate measurement oftemperatures. Methods and systems, in accordance with one or moreembodiments of the invention, are particularly suitable for hostileenvironments such as the interior of furnaces, e.g., reforming,annealing, metal or glass-making furnaces, etc., where measuring thetemperature of an object may be complicated by factors including theobject's emissivity, flame effects, reflection contributions,atmospheric effects and the geometry of the furnace, among others. Thetemperature measurements may be obtained for a single or many regions ofinterest, at any time and instantaneously.

A temperature measurement system, in accordance with one or moreembodiments of the invention, may be used for real-time monitoring andreal-time control of temperatures in industrial applications includingreformers, boilers, etc. In a reforming furnace the furnace temperaturemay be regulated based on the obtained temperature measurements tooptimize processes within the reformer furnace. In particular, thetemperature measurements may be used to minimize variations in reformertube wall temperatures, thereby avoiding potentially detrimentalhotspots, and to operate the reformer at a higher reformer temperaturewithout violating the maximum allowable reformer tube wall temperature.As a result, lifetime of the reformer tubes may increase, while theoperating point of the reformer may simultaneously improve, thusresulting, for example, in increased reformer output, reduced preheatingtimes, etc.

The system, in accordance with one or more embodiments of the invention,relies on one or more thermal imaging cameras that simultaneouslycapture data from all regions of interest (ROIs) in the furnace.Measurement accuracy may increase because the method does not requiremanually targeting a region of interest with a hand-held pyrometer.Because radiance measurements are instantaneously and simultaneouslyavailable from all ROIs, reliable temperature measurements may beobtained even in environments where dynamically changing temperatures inthe furnace do not allow a temperature measurement based on sequentiallytaken radiance measurements. Further, because the system does notrequire the opening of furnace doors in order to perform a radiancemeasurement, perturbations of the furnace atmosphere, associated withopening furnace doors, are avoided.

Temperature sensing solutions, in accordance with one or moreembodiments of the invention, in comparison to manually performedconventional temperature measurements, may be more cost effective, moreaccurate, may provide coverage of more regions of interest and may beperformed more frequently (e.g., rapidly and continuously) in anautomated manner, while reducing the risk for personnel.

Embodiments of the invention may be implemented on virtually any type ofcomputing system, regardless of the platform being used. For example,the computing system may be one or more mobile devices (e.g., laptopcomputer, smart phone, personal digital assistant, tablet computer, orother mobile device), desktop computers, servers, blades in a serverchassis, or any other type of computing device or devices that includesat least the minimum processing power, memory, and input and outputdevice(s) to perform one or more embodiments of the invention. Forexample, as shown in FIG. 5, the computing system (500) may include oneor more computer processor(s) (502), associated memory (504) (e.g.,random access memory (RAM), cache memory, flash memory, etc.), one ormore storage device(s) (506) (e.g., a hard disk, an optical drive suchas a compact disk (CD) drive or digital versatile disk (DVD) drive, aflash memory stick, etc.), and numerous other elements andfunctionalities. The computer processor(s) (502) may be an integratedcircuit for processing instructions. For example, the computerprocessor(s) may be one or more cores, or micro-cores of a processor.The computing system (500) may also include one or more input device(s)(510), such as a touchscreen, keyboard, mouse, microphone, touchpad,electronic pen, or any other type of input device. Further, thecomputing system (500) may include one or more output device(s) (508),such as a screen (e.g., a liquid crystal display (LCD), a plasmadisplay, touchscreen, cathode ray tube (CRT) monitor, projector, orother display device), a printer, external storage, or any other outputdevice. One or more of the output device(s) may be the same or differentfrom the input device(s). The computing system (500) may be connected toa network (512) (e.g., a local area network (LAN), a wide area network(WAN) such as the Internet, mobile network, or any other type ofnetwork) via a network interface connection (not shown). The input andoutput device(s) may be locally or remotely (e.g., via the network(512)) connected to the computer processor(s) (502), memory (504), andstorage device(s) (506). Many different types of computing systemsexist, and the aforementioned input and output device(s) may take otherforms.

Software instructions in the form of computer readable program code toperform embodiments of the invention may be stored, in whole or in part,temporarily or permanently, on a non-transitory computer readable mediumsuch as a CD, DVD, storage device, a diskette, a tape, flash memory,physical memory, or any other computer readable storage medium.Specifically, the software instructions may correspond to computerreadable program code that when executed by a processor(s), isconfigured to perform embodiments of the invention.

Further, one or more elements of the aforementioned computing system(500) may be located at a remote location and connected to the otherelements over a network (512). Further, one or more embodiments of theinvention may be implemented on a distributed system having a pluralityof nodes, where each portion of the invention may be located on adifferent node within the distributed system. In one embodiment of theinvention, the node corresponds to a distinct computing device.Alternatively, the node may correspond to a computer processor withassociated physical memory. The node may alternatively correspond to acomputer processor or micro-core of a computer processor with sharedmemory and/or resources.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

What is claimed is:
 1. A method for measuring furnace temperatures, themethod comprising: obtaining radiance measurements from a plurality ofregions of interest (ROls) of a furnace, using a plurality of thermalimaging cameras; measuring a surface temperature of the furnace using aradiance measurement obtained from an ROI selected from the plurality ofROIs, comprising: determining an effective background radiance affectingthe selected ROI, using radiance measurements obtained from ROIsdifferent from the selected ROI; obtaining a compensated radiance byremoving the effective background radiance from the radiance measurementobtained from the selected ROI; correcting the compensated radiance foran atmospheric absorption and an atmospheric emission; and convertingthe corrected compensated radiance to the measured surface temperatureof the furnace, wherein the correction for the atmospheric absorption isdetermined based on characteristics of the furnace atmosphere that istraversed for the radiance measurement of the selected ROI, thecharacteristics of the furnace atmosphere comprising at least oneselected from the group consisting of: the atmospheric distancetraversed between the ROI and the one or more thermal imaging cameras; alinear relationship between distance and atmospheric absorption; and alevel of water vapor in the furnace atmosphere, the correction for theatmospheric emission is determined based on characteristics of a flamefront that is traversed for the radiance measurement of the selectedROI, the characteristics of the flame front comprising at least oneselected from the group consisting of: a length of the traversed flamefront; a type of fuel fed to a burner generating the flame front; and afuel flow to the burner generating the flame front, and the correctionof the atmospheric emission is dynamically updated based on the fuelflow to the burner.
 2. The method of claim 1, wherein each of theplurality of ROIs is a surface region of the furnace on one selectedfrom a group consisting of a reformer tube, a wall, a floor, a ceilingand the flame front.
 3. The method of claim 1, wherein the radiancemeasurement obtained from the selected ROI is obtained from a pluralityof pixels in the ROI, averaged over at least one selected from the groupconsisting of space and time.
 4. The method of claim 1, wherein theradiance measurement obtained from the selected ROI is obtained from asingle pixel in the ROI.
 5. The method of claim 1, wherein a thermalimaging camera of a plurality of thermal imaging cameras obtainsradiance measurements from multiple ROIs that are a subset of theplurality of ROIs.
 6. The method of claim 1, wherein the radiancemeasurements are concurrently obtained; and wherein the surfacetemperature is measured in real-time.
 7. The method of claim 1, furthercomprising: adjusting the measured surface temperature to match areference surface temperature.
 8. The method of claim 1, whereindetermining the effective background radiance for the selected ROIcomprises: selecting surrounding surfaces that add reflected radiance tothe radiance measurement obtained from the selected ROI, wherein each ofthe surrounding surfaces comprises at least one ROI of the plurality ofROIs; determining mean radiances of the surrounding surfaces, based onradiance measurements from the at least one ROI on each of thesurrounding surfaces; and determining a weighted average of the meanradiances of the surrounding surfaces, wherein the weighted average isthe effective background radiance.
 9. The method of claim 8, wherein theweighted average is determined based on geometric view factors of thesurrounding surfaces.
 10. The method of claim 1, further comprising:correcting the radiance measurement obtained from the selected ROI foran emissivity of the selected ROI.
 11. The method of claim 10, whereinthe emissivity is determined through comparison of the radiancemeasurement obtained from the selected ROI with a radiance measurementobtained from a reference body with a known emissivity, wherein atemperature of the reference body with the known emissivity is identicalto a temperature of the ROI.
 12. A non-transitory computer readablemedium (CRM) storing instructions for measuring furnace temperatures,the instructions comprising functionality for: obtaining radiancemeasurements from a plurality of regions of interest (ROIs) of afurnace, using a plurality of thermal imaging cameras; measuring asurface temperature of the furnace using a radiance measurement obtainedfrom an ROI selected from the plurality of ROIs, comprising: determiningan effective background radiance affecting the selected ROI, usingradiance measurements obtained from ROIs different from the selectedROI; obtaining a compensated radiance by removing the effectivebackground radiance from the radiance measurement obtained from theselected ROI; correcting the compensated radiance for an atmosphericabsorption and an atmospheric emission; and converting the correctedcompensated radiance to the measured surface temperature of the furnace,wherein the correction for the atmospheric absorption is determinedbased on characteristics of the furnace atmosphere that is traversed forthe radiance measurement of the selected ROI, the characteristics of thefurnace atmosphere comprising at least one selected from the groupconsisting of: the atmospheric distance traversed between the ROI andthe one or more thermal imaging cameras; a linear relationship betweendistance and atmospheric absorption; and a level of water vapor in thefurnace atmosphere, the correction for the atmospheric emission isdetermined based on characteristics of a flame front that is traversedfor the radiance measurement of the selected ROI, the characteristics ofthe flame front comprising at least one selected from the groupconsisting of: a length of the traversed flame front; a type of fuel fedto a burner generating the flame front; and a fuel flow to the burnergenerating the flame front, and the correction of the atmosphericemission is dynamically updated based on the fuel flow to the burner.13. The non-transitory CRM of claim 12, wherein the radiancemeasurements are concurrently obtained; and wherein the surfacetemperature is measured in real-time.
 14. A system for measuring furnacetemperatures, comprising: a plurality of thermal imaging cameras; and aprocessing unit configured to: obtain radiance measurements from aplurality of regions of interest (ROIs) of a furnace, using a pluralityof thermal imaging cameras; measure a surface temperature of the furnaceusing a radiance measurement obtained from an ROI selected from theplurality of ROIs, comprising: determining an effective backgroundradiance affecting the selected ROI, using radiance measurementsobtained from ROIs different from the selected ROI; obtaining acompensated radiance by removing the effective background radiance fromthe radiance measurement obtained from the selected ROI; correcting thecompensated radiance for an atmospheric absorption and an atmosphericemission; and converting the corrected compensated radiance to themeasured surface temperature of the furnace, wherein the correction forthe atmospheric absorption is determined based on characteristics of thefurnace atmosphere that is traversed for the radiance measurement of theselected ROI, the characteristics of the furnace atmosphere comprisingat least one selected from the group consisting of: the atmosphericdistance traversed between the ROI and the one or more thermal imagingcameras; a linear relationship between distance and atmosphericabsorption; and a level of water vapor in the furnace atmosphere, thecorrection for the atmospheric emission is determined based oncharacteristics of a flame front that is traversed for the radiancemeasurement of the selected ROI, the characteristics of the flame frontcomprising at least one selected from the group consisting of: a lengthof the traversed flame front; a type of fuel fed to a burner generatingthe flame front; and a fuel flow to the burner generating the flamefront, and the correction of the atmospheric emission is dynamicallyupdated based on the fuel flow to the burner.
 15. The system of claim14, wherein the radiance measurements are concurrently obtained; andwherein the surface temperature is measured in real-time.
 16. A methodfor measuring furnace temperatures, the method comprising: obtainingradiance measurements from a plurality of regions of interest (ROIs) ofa furnace, using a plurality of thermal imaging cameras; measuring asurface temperature of the furnace using a radiance measurement obtainedfrom an ROI selected from the plurality of ROIs, comprising: determiningan effective background radiance affecting the selected ROI, usingradiance measurements obtained from ROIs different from the selectedROI; obtaining a compensated radiance by removing the effectivebackground radiance from the radiance measurement obtained from theselected ROI; and converting the compensated radiance to the measuredsurface temperature of the furnace, wherein the radiance measurementobtained from the selected ROI is obtained from a plurality of pixels inthe ROI, averaged over at least one selected from the group consistingof space and time.